Mycoplasmas are small prokaryotic organisms (0.2 to 0.3 μm) belonging to the class Mollicutes, whose members lack a cell wall and have a small genome size. The mollicutes include at least 100 species of Mycoplasma. Mycoplasma species are the causative agents of several diseases in human and non-human animals as well as in plants. M. gallisepticum, for example, is responsible for significant disease conditions in poultry. M. gallisepticum is associated with acute respiratory disease in chickens and turkeys and can also cause upper respiratory disease in game birds. In addition, M. gallisepticum has been recognized as a cause of conjunctivitis in house finches in North America.
An effective strategy for preventing and managing diseases caused by M. gallisepticum infection is by vaccination with live, attenuated strains of M. gallisepticum bacteria. The advantages of live attenuated vaccines, in general, include the presentation of all the relevant immunogenic determinants of an infectious agent in its natural form to the host's immune system, and the need for relatively small amounts of the immunizing agent due to the ability of the agent to multiply in the vaccinated host.
Live attenuated vaccine strains are often created by serially passaging a virulent strain multiple times in media. Although live attenuated vaccine strains against M. gallisepticum have been obtained by serial passaging, such strains are generally poorly characterized at the molecular level. It is assumed that attenuated strains made by serial passaging have accumulated mutations which render the microorganisms less virulent but still capable of replication. With regard to attenuated M. gallisepticum strains, however, the consequences of the mutations that result in attenuation (e.g., the identity of proteins whose expression pattern has been altered in the attenuated strain) are usually unknown.
Accordingly, a need exists in the art for new live, attenuated M. gallisepticum bacteria that have been characterized at the proteomic level and that are safe and effective in vaccine formulations.